The region in which the Cheslatta Lake showing occurs is within the Intermontane Belt, underlain dominantly by Lower to Middle Jurassic volcanic and sedimentary rocks of the Hazelton Group. These assemblages are overlain by the Upper Cretaceous to Lower Tertiary Ootsa Lake Group and Miocene plateau basalt. Intruding Lower Jurassic rocks of the Hazelton Group in the northeastern part of the map sheet is a belt of granodiorite, diorite and quartz diorite plutons of the Lower Jurassic Topley intrusive suite. Felsic plutons of probable Cretaceous age intrude both Lower and Middle Jurassic Hazelton strata.

The Ootsa Lake Group of Upper Cretaceous to Lower Tertiary age comprises mainly felsic volcanic rocks and their epiclastic derivatives. The Cheslatta Lake perlite showing occurs within a rhyolitic sequence of this group.